In the course of the operation of light-water nuclear reactors and, in particular, of pressurized-water nuclear reactors, there are carried out, during more or less prolonged shutdowns of the reactor, operations of recharging of the core consisting in replacing a part of the used fuel assemblies constituting the core. In the course of these recharging operations, there are also carried out the maintenance and the repair of certain items of internal equipment of the vessel of the reactor, in which vessel the core is placed.
During these operations, the vessel of the reactor is open and filled with water, just like the well of the reactor which surmounts and surrounds the vessel; this permits the operators carrying out the maintenance of the reactor to work on the elements situated within the vessel, from the service floor of the well of the reactor, with an effective biological protection consisting of a head of water of at least four meters.
The vessel of the reactor is liable to contain waste or debris which is highly radioactive and which may have become detached from the items of internal equipment or from the core, during the operation of the reactor or during the recharging or maintenance operations.
This debris or waste may consist, for example, of mechanical parts belonging to the internal structures of the reactor which have become damaged and detached during operation, under the effect of corrosion and of wear.
They may also consist of highly radioactive fuel pellets originating from a rod of a fuel assembly which may have been pierced or torn, either under the effect of corrosion in the reactor or as a result of attachment of the fuel assembly, in the course of its handling.
There is a risk that this waste or debris may constitute mobile bodies which are placed in circulation in the cooling fluid of the reactor when it is started up. These mobile bodies, which are entrained at very high speed by the cooling fluid, could damage the structures or to the core of the reactor and become lodged in an interstice, for example between two fuel rods.
Thus, there is a risk that the presence of mobile bodies will have an unfavorable effect on the operation of the reactor, with regard to both mechanical and thermal configurations.
It is therefore necessary to locate and to recover the waste or debris present in the vessel of the reactor, during the recharging and maintenance operations.
In order to recover the debris constituted by small mechanical parts which may be found wedged in the various parts of the fuel assemblies, a prior art device for the extraction of these foreign particles or parts comprises a grip which can be remotely controlled, from the edge of the well of the reactor. Such a device has is disclosed in French Patent Application 88-09025, assigned to FRAMATOME.
This extraction device, which takes the foreign body by gripping, does not permit the extraction of friable debris such as the fuel pellets which are subject to breakage when the grip is tightened. In the case of highly radioactive waste such as fuel pellets, there is a risk of contaminating the entire primary circuit.
It has also been proposed to use aspiration, filtration and delivery installations in which the water from the well is circulated, in order to filter the water and to retain the radioactive foreign bodies in the filter, before returning the water into the well of the reactor. However, in the case of highly radioactive bodies, the elimination of those bodies retained by the filter poses problems which are very difficult to resolve at the technical level. Moreover, the aspiration installation itself becomes contaminated after a certain operating time, so that it is very difficult to ensure its maintenance and its repair in the case of a break-down.